Update memmap2 requirement from 0.8 to 0.9 (#341)

Updates the requirements on [memmap2](https://github.com/RazrFalcon/memmap2-rs) to permit the latest version.
- [Changelog](https://github.com/RazrFalcon/memmap2-rs/blob/master/CHANGELOG.md)
- [Commits](RazrFalcon/memmap2-rs@v0.8.0...v0.9.0)

---
updated-dependencies:
- dependency-name: memmap2
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Cargo.toml

@@ -44,7 +44,7 @@ lazy_static = "1.3"
 libc = "0.2"
 log = { version = "0.4", features = ["max_level_trace", "release_max_level_debug"] }
 lz4-sys = "1.9"
-memmap2 = { version = "0.8", optional = true }
+memmap2 = { version = "0.9", optional = true }
 nix = "0.26"
 num-derive = "0.4"
 num-traits = "0.2"